Process for producing lactam

ABSTRACT

It is an object of the present invention to provide a method of continuously producing a lactam in high-temperature high-pressure water, and the present invention relates to a method for producing a lactam characterized by selectively synthesizing the lactam without bringing about hydrolysis by introducing an oxime into flowing high-temperature high-pressure water, wherein the lactam is continuously synthesized at a high rate from the oxime in water at a high temperature of at least 250° C. and a high pressure of at least 12 MPa.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of continuously producing alactam from an oxime in high-temperature high-pressure water, and moreparticularly to a novel continuous production method of continuouslyproducing a lactam by carrying out a rearrangement reaction of an oximein high-temperature high-pressure water without a catalyst. Yet morespecifically, there is provided a method that is favorable and useful asan industrial technique, enabling production of a lactam without theneed for treatment to neutralize a large amount of used waste sulfuricacid as seen in the case of a conventional production method in whichconcentrated sulfuric acid is used as a catalyst.

2. Description of the Related Art

Conventionally, a lactam such as E-caprolactam, which is used as a rawmaterial of nylon 6, is industrially produced by a Beckmannrearrangement from a carbonyl compound oxime such as cyclohexanoneoxime. An acid catalyst is used in this rearrangement reaction, andbecause the reaction is carried out while boiling, hydrolysis of theoxime will be brought about by the presence of even a very small amountof water in the system, resulting in a drop in the yield of the lactam.To prevent this, the usual method is to carry out the reaction whileboiling, using fuming sulfuric acid as the acid catalyst. With thismethod, because the reaction is carried out under harsh conditions,there are known to be problems with regard to corrosion of the materialsof the apparatus, the hazardousness of the production process, andprocessing of the byproduct ammonium sulfate. When recovering thelactam, the sulfuric acid used must be neutralized with ammonia, andmore than 2 kg of ammonium sulfate is produced as a byproduct per 1 kgof the lactam. Ammonium sulfate has little commercial value, and henceit is difficult to utilize the ammonium sulfate, and thus it has becomenecessary to process the ammonium sulfate.

In recent years, fears over deterioration of the global environment haveheightened, and in the chemical industry there have been calls for thedevelopment of environmentally friendly chemical processes that aresimple and efficient, according to which reaction can be completedwithin a short time, and according to which harmful substances are notused or not discharged. Regarding lactam production, there have beencalls for the development of a novel production process that isefficient, is not accompanied by byproducts, and does not useconcentrated sulfuric acid, with which there are problems in terms ofcorrosion of the materials of the apparatus, operational safety, and theenvironment.

As methods for resolving the above-problems, two methods have beenproposed in which reaction is carried out in high-temperaturehigh-pressure water and an acid catalyst such as sulfuric acid is notused at all, namely (1) a batch type synthesis method (O. Sato, Y.Ikushima and T. Yokoyama, Journal of Organic Chemistry 1998, 63,9100–9102), and (2) a flow type synthesis method (Y. Ikushima, K.Hatakeda, O. Sato, T. Yokoyama and M. Arai, Journal of American ChemicalSociety 2000, 122, 1908–1918).

With the batch type synthesis method (1), a reaction is carried out for3 minutes to obtain the product, wherein cyclohexanone oxime is sealedin a stainless steel tube of internal volume 10 ml, the stainless steeltube is put into a salt bath to rise the temperature thereof to 200 to400° C. within 30 seconds. It is considered that this method is notsuitable as a mass production process, but nevertheless the method hasattracted attention as a synthesis method that does not use an acidcatalyst such as fuming sulfuric acid. Operation of the reaction iscarried out intermittently to completion one batch at a time, and ittakes a time of approximately 20 to 30 seconds to raise the temperatureto the set reaction temperature. There is thus a drawback in that alarge amount of cyclohexanone as the hydrolysis product is producedwhile the temperature is being raised, and hence the yield of thetargeted ε-caprolactam is reduced. Moreover, cyclohexanone is a rawmaterial of cyclohexanone oxime, and hence the reaction goes in thereverse direction, which is fatal for an industrial process.

With the flow type synthesis method (2), operation of the reaction iscarried out continuously and hence it is considered that the method issuitable for mass production, but a cyclohexanone oxime aqueous solutionat room temperature is heated to produce the high-temperaturehigh-pressure carrier water in the reaction, and hence it seems thatraising the temperature up to the set reaction temperature takes a longtime. Accordingly, in an experiment in which reaction was carried outfor 113 seconds under conditions of 350° C. and 22.1 MPa, it wasrevealed that only cyclohexanone was obtained as a product, withε-caprolactam not being produced at all. Moreover, it is reported thatthe reaction is carried out even under conditions of 374.5° C.,ε-caprolactam and cyclohexanone are both produced. Consequently, itseems that, as with the batch type synthesis method (1), it takes timeto raise the temperature, and hence cyclohexanone is produced throughhydrolysis of the cyclohexanone oxime while the temperature of thesolvent water is passing from, for example, 100 to 300° C., and thusthere is a drawback in that the yield of the targeted ε-caprolactam isreduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofcontinuously producing a lactam in high-temperature high-pressure water.

The present invention relates to a method of producing a lactamcharacterized by selectively synthesizing the lactam by introducing anoxime into flowing high-temperature high-pressure water without bringingabout hydrolysis thereof, wherein the lactam is continuously synthesizedat a high rate from the oxime in water at a high temperature of at least250° C. and a high pressure of at least 12 MPa.

Amid the situation described above and in view of the prior artdescribed above, the present inventors carried out various studies intoa method of producing a lactam from an oxime in high-temperaturehigh-pressure water, and through this process discovered that tocontinuously and efficiently produce a lactam from an oxime inhigh-temperature high-pressure water, it is important to raise thetemperature of the oxime to the set reaction temperature within a shorttime; the present inventors then carried out further studies based onthis finding, thus accomplishing the present invention.

That is, the present invention was accomplished with an object ofproviding a method of selectively producing a lactam without producingcyclohexanone, by introducing an oxime as a substrate intohigh-temperature high-pressure water, thus carrying out reaction withthe time taken to raise the temperature of the substrate shortened.

The synthesis method of the present invention, which was developed bythe present inventors through various experiments, is, for example, amethod of producing caprolactam selectively and more efficiently and ina shorter time than with a conventional method, comprising continuouslyintroducing an oxime aqueous solution or an oxime directly into areaction zone in which there exists high-temperature high-pressurewater, whereby a set reaction temperature is reached within a shorttime, and hence hydrolysis of the oxime is suppressed.

To resolve the problems described above, the present invention isconstituted from the following technical means.

(1) A method for producing a lactam, comprising introducing oxime intohigh-temperature high-pressure water, raising the temperature of theoxime to put the oxime into a prescribed high-temperature high-pressurestate within a short time, and subjecting the oxime to a rearrangementreaction to obtain the lactam.

(2) The method for producing a lactam according to (1), wherein asubstrate aqueous solution having the oxime dissolved therein isintroduced into the continuously flowing high-temperature high-pressurewater, thus subjecting the oxime to the reaction in the prescribedhigh-temperature high-pressure state.

(3) The method for producing a lactam according to (1), wherein moltenoxime is introduced into the continuously flowing high-temperaturehigh-pressure water, thus subjecting the oxime to the reaction in theprescribed high-temperature high-pressure state.

(4) The method for producing a lactam according to any one of (1)through (3), wherein the oxime is subjected to the reaction in thehigh-temperature high-pressure water at a temperature of at least 250°C. and a pressure of at least 12 MPa.

(5) The method for producing a lactam according to any one of (1)through (4), wherein the temperature of the oxime is raised to put theoxime into the prescribed high-temperature high-pressure state within ashort time of not more than 3 seconds and the oxime is subjected to thereaction.

(6) The method for producing a lactam according to any one of (1)through (5), wherein the oxime is subjected to the reaction in theprescribed high-temperature high-pressure state for a time of not morethan 60 seconds.

(7) The method for producing a lactam according to any one of (1)through (6), wherein the oxime is cyclohexanone oxime.

Following is a more detailed description of the present invention.

To facilitate explanation of the present invention, a detaileddescription will be given taking as an example the case of producing alactam by introducing an oxime aqueous solution into high-temperaturehigh-pressure water, whereby a reaction temperature of 250 to 450° C. isreached within a short time of not more than 3 seconds, and reactiontakes place under a reaction pressure of 12 to 40 MPa.

The production method of the present invention, which was developed bythe present inventors through various experiments, is, for example, amethod in which a cyclohexanone oxime aqueous solution is continuouslyintroduced into a reaction zone through which high-temperaturehigh-pressure water is flowing, whereby the temperature thereof is madeto reach a set reaction temperature within a short time of not more than3 seconds, and hence ε-caprolactam is synthesized through arearrangement reaction of the cyclohexanone oxime, without bringingabout hydrolysis. In the present invention, high-temperaturehigh-pressure water is used as the reaction zone or reaction solvent;organic solvents and catalysts such as sulfuric acid are not used, anddo not need to be used. Consequently, according to the present method,waste matter that must be processed such as waste solvent, wastecatalyst and/or ammonium sulfate is not discharged. Moreover, there isno production of cyclohexanone through hydrolysis of the cyclohexanoneoxime. Unreacted raw material can be reused in the reaction of thepresent invention. Furthermore, with the method of the presentinvention, the product can be produced efficiently, continuously, and ata high rate, and hence the method of the present invention is consideredto be the best means of producing lactams.

Following is a description of the method of producing a lactam of thepresent invention.

In the present invention, for example, an oxime aqueous solution or anoxime is continuously introduced directly into a reaction zone in whichthere exists high-temperature high-pressure water, whereby thetemperature thereof is made to reach a set reaction temperature within ashort time, and hence a lactam can be produced efficiently with ashorter reaction time than with a conventional method, and selectivelywith hydrolysis of the oxime being suppressed.

An oxime used as the substrate raw material in the present invention isrepresented by general formula (1) (chemical formula 1), wherein n is aninteger from 1 to 9, and R₁ is hydrogen or an alkyl group. As an alkylgroup, any having 1 to 20 carbon atoms can be used, for example a methylgroup, an ethyl group, a propyl group or a butyl group. An example ofthe oxime is cyclohexanone oxime, but the present invention is notlimited to this.

A lactam obtained in the present invention is represented by generalformula (2) (chemical formula 2), wherein n is an integer from 1 to 9,and R₁ is hydrogen or an alkyl group. As an alkyl group, any having 1 to20 carbon atoms can be used, for example a methyl group, an ethyl group,a propyl group or a butyl group.

The lactam obtained in the present invention is a many-membered ringlactam having at least five members in the ring, for example a5-membered ring lactam, a 6-membered ring lactam or a 7-membered ringlactam. Examples include ε-caprolactam, γ-butyrolactam, γ-valerolactamand δ-valerolactam, but the present invention is not limited to these.

As a specific example of the production of a lactam according to thepresent invention, that is an example in which a 7-membered ring lactamis produced, general formula (3) (chemical formula 3) shows the reactionformula for synthesizing ε-caprolactam from cyclohexanone oxime.

It is known that the synthesis of a lactam through a Beckmannrearrangement of an oxime proceeds in the presence of an acid catalystThe fact that a lactam can be synthesized as in the present inventionthrough a Beckmann rearrangement of an oxime in high-temperaturehigh-pressure water is interesting matter. It can be conjectured that inhigh-temperature high-pressure water it may be that an acid catalystfunction appears through production of protons, polarization of thewater molecule structure, or the like, and it is expected that this willbe verified through physicochemical studies into high-temperaturehigh-pressure water in the future.

According to the present invention, the oxime that is the substrate canbe put into a prescribed high-temperature high-pressure state within ashort time, and hence hydrolysis can be suppressed, and thus a lactamcan be produced selectively. Note, however, that a small amount of anamino acid is produced through the present reaction. For example, in thecase of synthesizing ε-caprolactam from cyclohexanone oxime by reactingfor 0.667 seconds under a high temperature of 375° C. and high pressureof 30 MPa, the yield of ε-caprolactam was 41.4%, and compared with thisyield 6-aminocaproic acid was obtained at a yield of 0.3%. Conversion of6-aminocaproic acid into ε-caprolactam is relatively easy, and thisreaction also proceeds in high-temperature high-pressure water. In theabove reaction, the hydrolysis product cyclohexanone was not detected atall.

As the water used as the raw material of the high-temperaturehigh-pressure water in the present invention, distilled water, ionexchange water, tap water, ground water and so on can be favorably used.When using such a water as the raw material of the high-temperaturehigh-pressure water, in particular in the case of using thehigh-temperature high-pressure water in a super critical state,dissolved oxygen may cause oxidative decomposition of organic matter,and hence it is preferable to use the water after removing the dissolvedoxygen in advance by bubbling with nitrogen gas or the like. In the caseof using the high-temperature high-pressure water in a subcriticalstate, there is no particular need to remove dissolved oxygen from theraw material water, although this may be done.

The temperature of the high-temperature high-pressure water used in thepresent invention can be controlled using a heater, molten salt or thelike outside the reactor. Alternatively, this temperature control can becarried out using an internal heat means inside the reactor. Moreover,it is also possible to produce the high-temperature high-pressure waterin advance, and inject the high-temperature high-pressure water into thereactor from the outside using a conveying pump or the like for carryingout the reaction. It is also possible to feed two or more types ofhigh-temperature high-pressure water having different temperatures andpressures to one another into the reaction system, whereby the reactionconditions can be controlled. In the case that the flow system is used,the pressure inside the reaction vessel can be controlled using apressure regulating valve. Furthermore, the pressure can also becontrolled by injecting in another gas such as nitrogen gas. In generalthe pressure used should be at least the self-generated pressure at thetemperature used.

Basically, the present invention is realized so long as the reaction iscarried out in high-temperature high-pressure water at a temperature ofat least 250° C. and a pressure of at least 12 MPa. The presentinvention can be attained more favorably if the reaction is carried outin high-temperature high-pressure water at a temperature of at least300° C. and a pressure of at least 15 MPa. Furthermore, the presentinvention can be attained most favorably if the reaction is carried outin high-temperature high-pressure water at a temperature of at least350° C. and a pressure in a range of 15 MPa to 40 MPa. The idealtemperature varies according to the processing time, but in general atemperature in a range of 300° C. to 450° C. can be favorably selected.Moreover, an appropriate temperature and pressure can be adopted inaccordance with the throughput and the type of the reaction apparatus.With the present invention, it has been found that the reaction tends toproceed better if the temperature is higher, and moreover that thereaction also tends to be promoted somewhat by the pressure beinghigher.

As the reaction apparatus, for example a high-temperature high-pressurereaction apparatus can be used; however, there is no limitation thereto,but rather any type of apparatus can be used so long as the reaction canbe carried out in high-temperature high-pressure water. Here, asexamples of suitable reaction apparatuses, a flow type high-temperaturehigh-pressure reaction apparatus and flow type high-temperaturehigh-pressure reaction apparatus capable of introducing a molten oximeare used in the present invention.

In the present invention, an oxime aqueous solution or an oxime at, forexample, room temperature is directly introduced into flowinghigh-temperature high-pressure water, and hence the temperature of thehigh-temperature high-pressure water drops upon the mixing. The extentof the drop in temperature upon the mixing varies according to theinitial temperature of the carrier water, the reaction pressure, theflow rate of the carrier water, the flow rate of introduction of theoxime aqueous solution or oxime, the amount introduced of the oxime, thetype of the reactor, the volume of the reactor and so on. In general,from experience the set reaction temperature can be controlled bysuitably selecting the initial temperature of the carrier water to beapproximately 5 to 300° C. higher than the set reaction temperature.

The most distinctive feature of the present invention is that bydirectly introducing the oxime into high-temperature high-pressure waterat a temperature approximately 5 to 300° C. higher than the set reactiontemperature as described above, the time taken for the temperature ofthe oxime to rise to the set reaction temperature can be made to be ashort time of not more than 3 seconds. Due to this, hydrolysis of theoxime can be suppressed, and as a result the selectivity and yield ofthe lactam can be improved. The time taken for the temperature of theoxime to rise to the set reaction temperature is more preferably notmore than 1 second, yet more preferably not more than 0.5 seconds, mostpreferably not more than 0.3 seconds.

In the case of using the carrier water in a super critical state inparticular, the viscosity of the fluid is lower and the diffusioncoefficient is higher compared with that of general liquid carrierwater, and hence it is thought that the mixing rate is dramaticallyincreased. Moreover, it is known that with high-temperaturehigh-pressure water above a subcritical state close to the supercritical point, the dielectric constant is reduced and the solubility oforganic substances increases dramatically; it is thus thought that thesolubility of oximes similarly increases, resulting in conditionssuitable for the rearrangement reaction.

The reaction conditions vary according to the type and concentration ofthe oxime to be used, the volume of the reactor tube, the conditions ofthe high-temperature high-pressure water, and so on. In the presentinvention, there is no limitation to using one oxime in the reaction,but rather the reaction will still proceed favorably even if a mixtureof two or more oximes is used. The oxime can be melted and introducedinto the high-temperature high-pressure water and thus dissolvedtherein, or a powder of the oxime may be directly introduced into thehigh-temperature high-pressure water. Alternatively, a substrate aqueoussolution in which the oxime has been dissolved in advance at roomtemperature can be introduced into the high-temperature high-pressurewater.

The concentration of the oxime to be introduced into the reactor can becontrolled by controlling the flow rate of the high-temperaturehigh-pressure water to be used as the flowing carrier water and the flowrate of introduction of the reaction substrate oxime. In general, theconcentration of the oxime to be introduced into the reactor is selectedfrom a concentration range of 1 mM to 10 M. It is preferable to select asuitable concentration value from 2 mM to 5 M, and most preferable toselect a suitable concentration value from 2 mM to 2 M, although thereis no limitation to these concentration ranges in the present invention.

In the present invention, the reaction yield of the lactam can bemanipulated by adjusting the temperature and pressure of the reactionsystem, the internal diameter of the reactor, the volume of the reactor,the flow rates, the concentration of the reaction substrate, thereaction time and so on, this being in accordance with the type of theoxime.

Regarding the reaction system in the present invention, the reactionsubstrate oxime need merely be made to be present in high-temperaturehigh-pressure water at a temperature of at least 250° C. and a pressureof at least 12 MPa as described above; at this time, there is noparticular need to add, for example, metal ions, a water-solublecatalyst such as an acid or a base, a metal-supporting catalyst, a solidcatalyst such as a solid acid or a solid base, an enzyme, or the like,and moreover there is also no need to use an organic solvent.

Basically, the most distinctive feature of the present invention is thata lactam is synthesized from an oxime by making a reaction substrate asdescribed above be present in high-temperature high-pressure water,without a catalyst, and without an organic solvent being involved in thereaction; nevertheless, if necessary, it is quite acceptable to add anorganic solvent such as methanol, ethanol or ethylene glycol, metalions, a water-soluble catalyst such as an acid or a base, ametal-supporting catalyst, a solid catalyst such as a solid acid or asolid base, or an enzyme when carrying out the reaction.

In the present invention, using the reaction system described above, alactam is synthesized from an oxime within a short time, i.e. with areaction time of, for example, 0.001 seconds to 60 seconds. In the caseof using a flow type reaction apparatus, the reaction time can becontrolled by controlling,the reaction temperature, the reactionpressure, the flow rate of the high-temperature high-pressure water, theflow rate of introduction of the reaction substrate, the shape of thereactor, the internal diameter of the reactor, the length of the flowpath of the reactor, and so on. The reaction time is more preferablyselected from a range of 0.01 seconds to 30 seconds, and is mostpreferably selected from a range of 0.05 seconds to 10 seconds, althoughthere is no limitation to these ranges in the present invention.

As shown in the examples described later, using a high performanceliquid chromatography-mass spectrometry (LC-MS) apparatus, a nuclearmagnetic resonance (NMR) spectrometer and a Fourier transform infrared(FTIR) spectrophotometer, the present inventors have verified that it ispossible to carry out a rearrangement reaction from an oxime to a lactamwithin a short time (e.g. a reaction time of approximately 1 second) inhigh-temperature high-pressure water. Furthermore, by using an LC-MSapparatus, the types of the oxime, the lactam, and the byproduct aminoacid can be identified, and the contents thereof can be measuredaccurately. Moreover, by subjecting the continuously obtained lactam toseparation and purification using an ion exchange resin column,measuring the infrared absorption spectrum using an FTIRspectrophotometer, and comparing with the infrared absorption spectra ofhigh-purity special grade reagent products, the lactam can be identifiedaccurately. Similarly, the type and purity of the lactam can also beverified by NMR spectroscopy. The structure of the lactam can beverified using a gas chromatography-mass spectrometry (GC-MS) apparatus,an LC-MS apparatus, an NMR spectrometer, and an FTIR spectrophotometer.

The reaction yield of the lactam produced in the present inventionvaries according to the reaction conditions such as the temperature andthe pressure, the type of the oxime, the concentration of the oxime, theform of the reaction apparatus, the size of the reactor, the flow rateof the carrier water, the rate of introduction of the oxime, thereaction time, and so on. For example, in the case of ε-caprolactam, thereaction yield was from 5.5% to 76.3%. The ε-caprolactam is recoveredmixed together with the raw material cyclohexanone oxime. Similarly,according to the present invention, any of various lactams obtained fromany of various oximes or a mixture thereof are recovered together withthe raw material substrates, but by using, for example, a cationexchange resin, an anion exchange resin, or a combination thereof, thelactam and the raw material substrate oxime can be separated, andmoreover in the case of obtaining a plurality of lactams the lactams canbe separated from one another, and hence the lactams can be purified andconcentrated type by type. Moreover, the oximes recovered at the sametime can be reused as raw material.

It is thus possible to synthesize lactam by subjecting oxime to arearrangement reaction in high-temperature high-pressure water, andsubject the reaction solution obtained to an ion exchange resin toseparate and purify the lactam, whereby high-purity lactam can befavorably produced.

In the present invention, a prescribed concentration of an oxime isintroduced as a reaction substrate into high-temperature high-pressurewater, thus raising the temperature of the reaction substrate within ashort time, and carrying out reaction in a prescribed high-temperaturehigh-pressure aqueous state, whereby, for example, ε-caprolactam issynthesized from cyclohexanone oxime. Moreover, by continuouslyintroducing such oximes into flowing high-temperature high-pressurewater, various lactams corresponding to the respective oximes can besynthesized continuously.

As described above, the present invention is a novel continuous lactamproduction method that enables any of various lactams to be producedcontinuously within a short time using the reaction system describedabove by adjusting the reaction conditions, the type of the reactionsubstrate oxime, and the concentration of the oxime, and is thus usefulas a lactam production method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an arrangement of a flow type high-temperaturehigh-pressure reaction apparatus having two conveying pumps used in thepresent invention; and

FIG. 2 shows an arrangement of a molten oxime introduction type flowtype high-temperature high-pressure reaction apparatus having twoconveying pumps used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Following is a concrete description of the present invention throughexamples; however, the present invention is not limited whatsoever bythe following examples.

EXAMPLE 1

Using a continuous type high-temperature high-pressure reactionapparatus as shown in FIG. 1, continuous production of ε-caprolactamthrough a rearrangement reaction was attempted using a cyclohexanoneoxime (purity 97%) made by Aldrich Chemical Company, Inc. inhigh-temperature high-pressure water of temperature 375° C., pressure 30MPa and density 0.5583 g/cm³.

The material of the reactor was alloy C-276, and the internal diameterof the reactor was 0.325 mm and the length of the reactor was 120 cm,and hence the volume of the reactor was calculated to be 0.0995 cm³.Each of the prepared liquids to be introduced (i.e. the carrier waterand the cyclohexanone oxime substrate solution) was injected in using ahigh-pressure pump. Distilled water from which dissolved oxygen had beendriven out by bubbling with nitrogen gas was heated to produce carrierwater at 460° C. and 30 MPa, and the carrier water was passed through ata flow rate of 3.8 ml/min. A 21.9 mM cyclohexanone oxime substratesolution was prepared using similarly deoxygenated distilled water. Thesubstrate solution was introduced at room temperature and 30 MPa intothe carrier water at the reactor inlet at a flow rate of 1.3 ml/min,thus mixing the substrate solution and the carrier water together. Thereaction temperature of the mixed solution measured by a thermocouple(1) installed 1 cm from the reactor inlet was 375° C., which matched thetemperature measured by a thermocouple (2) at the reactor outlet, andhence it is inferred that the temperature throughout the reactor wasconstant, and that the carrier water and the substrate solution weremixed together homogeneously. The substrate concentration after themixing was 5.58 mM. The reaction time was 0.667 seconds. It is thusinferred that the mixing took place within a short time of not more than0.006 seconds. The aqueous solution recovered after the reaction wasexamined using a high performance liquid chromatography-massspectrometry apparatus, whereupon it was found that ε-caprolactam as amain product and 6-aminocaproic acid as a byproduct had been produced.Apart from that, only unreacted cyclohexanone oxime was detected, withcyclohexanone, which is the hydrolysis product of the raw material, notbeing detected at all. The concentration of the ε-caprolactam was 2.31mM, and hence the reaction yield thereof was 41.4%. The concentration ofthe 6-aminocaproic acid was 0.017 mM, and hence the reaction yieldthereof was 0.3%.

EXAMPLE 2

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 404° C., 25 MPa-   Flow rate of carrier water: 3.7 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 25    MPa-   Flow rate of 21.9 mM substrate solution: 1.3 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    350° C.-   Pressure of high-temperature high-pressure water to be reacted: 25    MPa-   Density of high-temperature high-pressure water to be reacted:    0.6257 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was5.69 mM. The reaction time was 0.747 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.006 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 1.61 mM, and hence the reactionyield thereof was 28.3%. The concentration of the 6-aminocaproic acidwas 0.011 mM, and hence the reaction yield thereof was 0.2%.

EXAMPLE 3

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 352° C., 15 MPa-   Flow rate of carrier water: 2.9 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 15    MPa-   Flow rate of 21.9 mM substrate solution: 2.1 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    300° C.-   Pressure of high-temperature high-pressure water to be reacted: 15    MPa-   Density of high-temperature high-pressure water to be reacted:    0.7259 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was9.20 mM. The reaction time was 0.867 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing together of the carrier water and the substrate solution tookplace within a short time of not more than 0.007 seconds. The aqueoussolution after the reaction was examined using a high performance liquidchromatography-mass spectrometry apparatus, whereupon it was found thatε-caprolactam had been produced as a product. Apart from that, onlyunreacted cyclohexanone oxime was detected, with cyclohexanone, which isthe hydrolysis product of the raw material, not being detected at all.The concentration of the ε-caprolactam was 0.51 mM, and hence thereaction yield thereof was 5.5%.

COMPARATIVE EXAMPLE 1

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 314° C., 15 MPa-   Flow rate of carrier water: 3.5 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 15    MPa-   Flow rate of 21.9 mM substrate solution: 1.4 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    200° C.-   Pressure of high-temperature high-pressure water to be reacted: 15    MPa-   Density of high-temperature high-pressure water to be reacted:    0.8746 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 4.9    ml/min

The cyclohexanone oxime substrate concentration after the mixing was6.26 mM. The reaction time was 1.066 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing together of the carrier water and the substrate solution tookplace within a short time of not more than 0.009 seconds. The aqueoussolution after the reaction was examined using a high performance liquidchromatography-mass spectrometry apparatus, whereupon production ofε-caprolactam was not detected at all.

COMPARATIVE EXAMPLE 2

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 345° C., 9 MPa-   Flow rate of carrier water: 3.3 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 9    MPa-   Flow rate of 21.9 mM substrate solution: 1.7 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    300° C.-   Pressure of high-temperature high-pressure water to be reacted: 9    MPa-   Density of high-temperature high-pressure water to be reacted:    0.7134 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was7.45 mM. The reaction time was 0.852 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing together of the carrier water and the substrate solution tookplace within a short time of not more than 0.007 seconds. The aqueoussolution after the reaction was examined using a high performance liquidchromatography-mass spectrometry apparatus, whereupon production ofε-caprolactam was not detected at all.

EXAMPLE 4

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 550° C., 25 MPa-   Flow rate of carrier water: 4.6 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 25    MPa-   Flow rate of 21.9 mM substrate solution: 0.5 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    400° C.-   Pressure of high-temperature high-pressure water to be reacted: 25    MPa-   Density of high-temperature high-pressure water to be reacted:    0.1666 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.1    ml/min

The cyclohexanone oxime substrate concentration after the mixing was2.15 mM. The reaction time was 0.195 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.002 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 0.19 mM, and hence the reactionyield thereof was 8.8%. The concentration of the 6-aminocaproic acid was0.002 mM, and hence the reaction yield thereof was 0.1%.

EXAMPLE 5

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 550° C., 40 MPa-   Flow rate of carrier water: 3.7 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 40    MPa-   Flow rate of 21.9 mM substrate solution: 1.3 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    400° C.-   Pressure of high-temperature high-pressure water to be reacted: 40    MPa-   Density of high-temperature high-pressure water to be reacted:    0.5237 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was5.69 mM. The reaction time was 0.625 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.005 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 3.78 mM, and hence the reactionyield thereof was 66.4%. The concentration of the 6-aminocaproic acidwas 0.078 mM, and hence the reaction yield thereof was 1.4%.

EXAMPLE 6

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 550° C., 40 MPa-   Flow rate of carrier water: 4.2 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 40    MPa-   Flow rate of 21.9 mM substrate solution: 0.8 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    420° C.-   Pressure of high-temperature high-pressure water to be reacted: 40    MPa-   Density of high-temperature high-pressure water to be reacted:    0.4238 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 5.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was3.50 mM. The reaction time was 0.506 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.004 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 1.58 mM, and hence the reactionyield thereof was 45.1%. The concentration of the 6-aminocaproic acidwas 0.028 mM, and hence the reaction yield thereof was 0.8%.

EXAMPLE 7

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 475° C., 40 MPa-   Flow rate of carrier water: 15.6 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 40    MPa-   Flow rate of 21.9 mM substrate solution: 4.4 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    375° C.-   Pressure of high-temperature high-pressure water to be reacted: 40    MPa-   Density of high-temperature high-pressure water to be reacted:    0.6096 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted:    20.0 ml/min

The cyclohexanone oxime substrate concentration after the mixing was4.82 mM. The reaction time was 0.182 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.002 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 1.31 mM, and hence the reactionyield thereof was 27.2%. The concentration of the 6-aminocaproic acidwas 0.023 mM, and hence the reaction yield thereof was 0.5%.

EXAMPLE 8

Reaction was carried out as in Example 1, thus attempting continuousproduction of ε-caprolactam through a rearrangement reaction ofcyclohexanone oxime. The reaction conditions, however, were changed tothe following.

Reaction Conditions

-   Temperature and pressure of carrier water: 475° C., 40 MPa-   Flow rate of carrier water: 1.4 ml/min-   Temperature and pressure of 21.9 mM substrate solution: 25° C., 40    MPa-   Flow rate of 21.9 mM substrate solution: 0.6 ml/min-   Temperature of high-temperature high-pressure water to be reacted:    375° C.-   Pressure of high-temperature high-pressure water to be reacted: 40    MPa-   Density of high-temperature high-pressure water to be reacted:    0.6096 g/cm³-   Flow rate of high-temperature high-pressure water to be reacted: 2.0    ml/min

The cyclohexanone oxime substrate concentration after the mixing was4.82 mM. The reaction time was 1.820 seconds, and the temperaturethroughout the reactor was constant, and hence it is inferred that themixing took place within a short time of not more than 0.015 seconds.The aqueous solution after the reaction was examined using a highperformance liquid chromatography-mass spectrometry apparatus, whereuponit was found that ε-caprolactam as a main product and 6-aminocaproicacid as a byproduct had been produced. Apart from that, only unreactedcyclohexanone oxime was detected, with cyclohexanone, which is thehydrolysis product of the raw material, not being detected at all. Theconcentration of the ε-caprolactam was 3.68 mM, and hence the reactionyield thereof was 76.3%. The concentration of the 6-aminocaproic acidwas 0.132 mM, and hence the reaction yield thereof was 2.7%.

EXAMPLE 9

Using a continuous type reaction apparatus as shown in FIG. 2,continuous production of ε-caprolactam through a rearrangement reactionwas attempted by introducing a melt of cyclohexanone oxime (purity 97%)made by Aldrich Chemical Company, Inc. into high-temperaturehigh-pressure water of temperature 350° C., pressure 30 MPa and density0.6443 g/cm³.

The material of the reactor was alloy C-276, and the internal diameterof the reactor was 4.68 mm and the length of the reactor was 200 mm, andhence the volume of the reactor was calculated to be 3.440 cm³. Each ofthe prepared liquids to be introduced (i.e. the carrier water and thesubstrate melt) was injected in using a high-pressure pump. Distilledwater from which dissolved oxygen had been driven out by bubbling withnitrogen gas was heated to produce carrier water at 357° C. and 30 MPa,and the carrier water was passed through at a flow rate of 24.6 ml/min.The cyclohexanone oxime was heated on 95° C. to prepare the substratemelt. The substrate melt was pressurized to 30 MPa using pressurizedwater and introduced into and thus mixed with the carrier water at thereactor inlet at a flow rate of 0.4 ml/min. The reaction temperature ofthe mixed solution measured by a thermocouple (1) installed 1 cm fromthe reactor inlet was 350° C., which matched the temperature measured bya thermocouple (2) at the reactor outlet, and hence it is inferred thatthe temperature throughout the reactor was constant, and that thecarrier water and the substrate melt were mixed together homogeneously.The substrate concentration after the mixing was 141.6 mM. The reactiontime was 5.165 seconds. It is thus inferred that the mixing anddissolution was completed within a short time of not more than 0.258seconds. The aqueous solution after the reaction was examined using ahigh performance liquid chromatography-mass spectrometry apparatus,whereupon it was found that ε-caprolactam as a main product and6-aminocaproic acid as a byproduct had been produced. Apart from that,only unreacted cyclohexanone oxime was detected, with cyclohexanone,which is the hydrolysis product of the raw material, not being detectedat all. The concentration of the ε-caprolactam was 96.8 mM, and hencethe reaction yield thereof was 68.4%. The concentration of the6-aminocaproic acid was 2.1 mM, and hence the reaction yield thereof was1.5%.

COMPARATIVE EXAMPLE 3

A thermocouple was connected to a SUS316 tubular reactor of internaldiameter 8.7 mm and length 170 mm (internal volume 10.1 cm³), and anexperiment of synthesizing ε-caprolactam from cyclohexanone oxime usinga batch type reaction method was carried out by rapidly raising thetemperature thereof using a molten salt bath to 375° C. to react it for3 minutes. Specifically, 3.5 g of distilled water and 0.5 g ofcyclohexanone oxime were put into the reactor, and the reactor wassealed in a stream of nitrogen. The reactor was put into a molten saltbath the temperature of which had already been set to 375° C., wherebythe reactor was heated to the set reaction temperature. The pressure atthe reaction temperature was determined by calculation from the internalvolume, the amount of water used, and the temperature, using the vaporpressure curve for water. After carrying out reaction for 3 minutes at375° C., the reaction was stopped by putting the reactor into a coldwater bath. The reaction pressure was 25 MPa, and the time taken for thetemperature to rise to 375° C. was 29 seconds.

After the cooling the reaction mixture, the products in the reactor wererecovered using water and chloroform, the organic solvent layer wasseparated off, and then the organic solvent was distilled off. Theproducts were examined using mass spectroscopy, nuclear magneticresonance spectroscopy and gas chromatography. The results of theanalysis were that the yield of ε-caprolactam was 14.7% and the yield ofcyclohexanone was 45.8%. With this batch type synthesis method, a largeamount of cyclohexanone, which is the hydrolysis product ofcyclohexanone oxime, was produced, and hence it is considered that themethod is not suitable as an industrial process.

INDUSTRIAL APPLICABILITY

As described in detail above, the present invention relates to acontinuous lactam production method in which a lactam is continuouslysynthesized without bringing about hydrolysis by introducing an oximeinto flowing high-temperature high-pressure water, that is a continuouslactam production method in which a lactam is produced selectively froman oxime in high-temperature high-pressure water. According to thepresent invention, the following remarkable effects are attained: 1) alactam can be produced selectively from an oxime by suppressinghydrolysis of the oxime in high-temperature high-pressure water; 2) alactam can be produced within a short time by reacting an oxime underhigh temperature and high pressure; 3) a method of producing a lactam inwhich a catalyst is not used at all can be provided; and 4) the chemicalsubstance production system which is environmentally friendly isprovided.

1. A method for continuously producing caprolactam, comprisingintroducing an oxime into high-temperature high pressure water, raisingthe temperature of the oxime to put the oxime into a prescribedhigh-temperature high-pressure state within a short time, and subjectingthe oxime to a rearrangement reaction to obtain the lactam; wherein thetemperature of the high-temperature high-pressure state is at least 375°C.; wherein the pressure of the high-temperature high pressure water isat least 40 MPa; wherein the raising the temperature of the oxime occursin less than or equal to 0.3 seconds; and wherein the oxime has theformula (1)

wherein n is 3, and R₁ is hydrogen or an alkyl group.
 2. The method forproducing caprolactam according to claim 1, wherein a substrate aqueoussolution having the oxime dissolved therein is introduced into thecontinuously flowing high-temperature high-pressure water, thussubjecting the oxime to the reaction in the prescribed high-temperaturehigh-pressure state.
 3. The method for producing caprolactam accordingto claim 1, wherein molten oxime is introduced into the continuouslyflowing high-temperature high-pressure water, thus subjecting the oximeto the reaction in the prescribed high-temperature high-pressure state.4. The method for producing caprolactam according to any one of claims 1through 3, wherein the oxime is subjected to the reaction in theprescribed high-temperature high-pressure state for a time of not morethan 60 seconds.
 5. The method for producing a lactam according to claim4, wherein the oxime is subjected to the reaction in the prescribedhigh-temperature high-pressure state for a time of from 0.001 seconds to60 seconds.
 6. The method of claim 1, wherein R₁ is a radical selectedfrom the group consisting of methyl, ethyl, propyl, and butyl.